Concentration measuring method and concentration measuring device

ABSTRACT

The present invention relates to a technique for measuring the concentration of a particular component in a sample liquid using a test tool ( 2 ). The test tool ( 2 ) includes a first through a third detection elements ( 31   a - 33   a ) arranged in the mentioned order in the moving direction of the sample liquid for measuring an electro-physical quantity. The present invention provides a concentration measuring method which includes a first detection step for detecting whether or not liquid conduction is established between the first and the second detection elements ( 31   a   , 32   a ), a second detection step for detecting whether or not liquid conduction is established between the second and the third detection elements ( 31   a   , 33   a ), a measurement step for measuring an electro-physical quantity by using the first through the third detection elements ( 31   a - 33   a ), and a concentration computation step for computing the concentration of the particular component based on the electro-physical quantity. The present invention also provides a concentration measuring apparatus ( 1 ) for realizing the concentration measuring method.

TECHNICAL FIELD

[0001] The present invention relates to a technique for measuring theconcentration of a particular component (e.g. glucose or cholesterol)contained in a sample liquid (e.g. blood or urine).

BACKGROUND ART

[0002] A popular method for measuring the concentration of a particularcomponent contained in a sample liquid (e.g. glucose in blood) utilizesoxidation-reduction reaction. Portable hand-held blood glucose levelmeasuring apparatuses are available so that the user can easily checkthe blood glucose level while staying at home or away from home. Tomeasure the blood glucose level using such a portable blood glucoselevel measuring apparatus, a disposable biosensor for providing anenzyme reaction system is attached to the measuring apparatus, and thenblood is supplied to biosensor for the measurement of the blood glucoselevel (See JP-B-8-10208, for example).

[0003] Various types of biosensors have been put to practical use, anexample of which is shown in FIGS. 11 and 12 of the accompanyingdrawings. The illustrated biosensor 9 includes a substrate 92, a spacer93, a cover 94, and a capillary 95 defined by these parts. The substrate92 is formed with an operative electrode 90 and a counterpart electrode91. A portion 90 a of the operative electrode 90 and a portion 91 a ofthe counterpart electrode 91 are located within the capillary 95 andconnected to each other by a reagent portion 96. The reagent portion 96contains oxidoreductase and an electron carrier. The cover 94 is formedwith a discharge port 94 a and laminated on the substrate 92 via thespacer 93. The interior of the capillary 95 communicates with theoutside through an open end 93 a of a slit 93A and the discharge port 94a.

[0004] For measuring the blood glucose level, blood is introduced to thecapillary 95 of the biosensor 9, which is pre-mounted to the bloodglucose level measuring apparatus. The blood moves through the capillary95 to the discharge port 94 a by capillary action while dissolving thereagent portion 96 to form a liquid phase reaction system in thecapillary 95. The concentration measuring apparatus determines whetheror not the sample liquid introduced into the capillary 95 based on tothe response current (or the voltage converted from the responsecurrent) obtained by utilizing the operative electrode 90 and thecounterpart electrode 91. Specifically, when the response current (orthe responsive voltage) is equal to or higher than a predeterminedthreshold value, it is determined that the blood is supplied.

[0005] In the liquid phase reaction system in the capillary 95, theglucose in the blood is oxidized while the electron carrier is reducedby the catalytic reaction of oxidoreductase. When certain voltage isapplied to the liquid phase reaction system, the electron carrier isoxidized (releases electrons), and the electrons released by theelectron carrier is supplied to the operative electrode 90. The bloodglucose level measuring apparatus measures the supply of electrons tothe operative electrode 90 as the oxidation current, and computes theglucose level based on the oxidation current.

[0006] The response current reflects the supply of electrons to theoperative electrode 90, and the electron supply to the operativeelectrode 90 reflects the amount of oxidized glucose,

[0007] i.e. the glucose level. However, the blood contains blood cellcomponents such as red blood cells, and the response current variesdepending on the amount of the blood cell components. The amount ofblood cell components in blood (hematocrit) differs among individualsand varies depending on physical condition even in the same person.Therefore, due to the influence of hematocrit, proper measurement may beimpossible even when the same person performs measurement, let alonewhen the users are different. Further, the response current measured maybe influenced not only by hematocrit but also by the degree of chyle orhemolysis of blood, for example.

[0008] The influence of hematocrit may be eliminated by a method inwhich the hematocrit of the blood is measured in advance and the bloodglucose level is calculated while taking the hematocrit intoconsideration (See JP-A-11-194108, for example).

[0009] However, the concentration measurement by such a method istroublesome, because the hematocrit need be inputted in the bloodglucose level measuring apparatus. The operation for inputtinghematocrit is particularly troublesome in a medical facility, forexample, in which a single blood glucose level measuring apparatus needbe used frequently for measuring the blood glucose level of a largenumber of patients. Moreover, before the use of the blood glucose levelmeasuring apparatus, another apparatus need be used for measuring thehematocrit of the patient, which makes the method further troublesome.

DISCLOSURE OF THE INVENTION

[0010] An object of the present invention is to make it possible toperform proper concentration measurement while taking the influence ofanother component contained in the sample liquid into consideration andavoiding posing a burden on the user.

[0011] According to a first aspect of the present invention, there isprovided a concentration measuring method for measuring concentration ofa particular component in a sample liquid using a test tool whichcomprises a capillary for moving the sample liquid, and a first throughthird detection elements for measuring an electro-physical quantity. Thefirst through the third detection elements are arranged in the mentionedorder from an upstream side toward a downstream side in the movingdirection of the sample liquid. The method comprises a first detectionstep for detecting whether or not liquid conduction is establishedbetween the first detection element and the second detection element, asecond detection step for detecting whether or not liquid conduction isestablished between the second detection element and the third detectionelement, a measurement step for measuring an electro-physical quantityfor computation by using at least two of the first through the thirddetection elements, and a concentration computation step for computingthe concentration of the particular component based on theelectro-physical quantity for computation.

[0012] Examples of electro-physical quantity include current, voltageand resistance.

[0013] Preferably, the concentration measuring method of the presentinvention further comprises a time computation step for computing timetaken from the detection of liquid conduction in the first detectionstep to the detection of liquid conduction in the second conductionstep. In this case, the concentration computation step preferablycomprises computing the concentration of the particular component whiletaking the computed time into consideration.

[0014] The concentration computation step may include data processingoperation for correcting, based on a correction value, anelectro-physical quantity for computation or a computed value obtainedbased on the electro-physical quantity for computation.

[0015] The computed value may be a voltage converted from a responsecurrent measured as the electro-physical quantity, or the concentrationobtained by computation without correction. The correction value may beobtained by computation based on data showing a relationship between thetime taken and a correction value.

[0016] Preferably, the second detection step comprises measuring anelectro-physical quantity by using all of the first through the thirddetection elements and determining whether or not liquid conduction isestablished between the second detection element and the third detectionelement based on a time history of the electro-physical quantity.

[0017] Specifically, for example, the second detection step comprisesmeasuring an electro-physical quantity at a plurality of predeterminedmeasurement time points, computing a variation in current per unit timeat each of the measurement time points, and determining that liquidconduction is established between the second detection element and thethird detection element when the variation in current is greater than apredetermined threshold value.

[0018] The second detection step may comprise computing a differencebetween an electro-physical quantity measured at a certain measurementtime point and an electro-physical quantity measured at anothermeasurement time point directly before said certain measurement timepoint and determining that liquid conduction is established between thesecond detection element and the third detection element when thedifference is greater than a predetermined threshold value.

[0019] Preferably, the third detection element is larger in surface areathan the first detection element in the test tool.

[0020] Preferably, the concentration computation step comprisescomputing the concentration of the particular component based on adifference between an electro-physical quantity measured after apredetermined time has elapsed since liquid conduction between thesecond detection element and the third detection element was detected inthe second detection step and another electro-physical quantity measuredwhen liquid conduction between the second detection element and thethird detection element is detected in the second step.

[0021] For example, the sample liquid may contain a coexisting componentwhich causes an error in the concentration measurement of the particularcomponent. In this case, the time taken is figured out as a reflectionof influence of the coexisting component. When the sample liquid isblood, the coexisting component which causes a measurement error may beblood cells, and the particular component may be glucose. The sampleliquid may be other biochemical samples such as urine or saliva, orsamples other than biochemical samples.

[0022] According to a second aspect of the present invention, there isprovided a concentration measuring apparatus for measuring concentrationof a particular component in a sample liquid using a test tool whichcomprises a capillary for moving the sample liquid, and a first througha third detection elements for measuring an electro-physical quantity.The first through the third detection elements are arranged in thementioned order from an upstream side toward a downstream side in themoving direction of the sample liquid. The apparatus comprises adetector for detecting whether or not liquid conduction is establishedbetween the first detection element and the second detection element aswell as between the second detection element and the third detectionelement, an electro-physical quantity measurer for measuring anelectro-physical quantity for computation by using at least two of thefirst through the third detection elements, and a computation unit forcomputing the concentration of the particular component based on theelectro-physical quantity for computation.

[0023] Preferably, the concentration measuring apparatus furthercomprises a voltage application unit for applying a voltage across atleast two detection elements selected from the first through the thirddetection elements. In this case, the electro-physical quantity measurermeasures a current as the electro-physical quantity when the voltageapplication means applies the voltage. Alternatively, theelectro-physical quantity measurer may measure e.g. resistance as theelectro-physical quantity.

[0024] Preferably, the computation unit computes the time taken from theestablishment of liquid conduction between the first detection elementand the second detection element to the establishment of liquidconduction between the second detection element and the third detectionelement and computes the concentration of the particular component whiletaking the computed time into consideration.

[0025] For example, the electro-physical quantity measurer measures anelectro-physical quantity at a plurality of measurement time points withpredetermined intervals. Preferably, in this case, the detectordetermines whether or not liquid conduction is established between thesecond detection element and the third detection element based on atime-course of the electro-physical quantity.

[0026] Specifically, for example, the detector computes a variation incurrent per unit time at each of the measurement time points anddetermines that liquid conduction is established between the seconddetection element and the third detection element when the variation incurrent is greater than a predetermined threshold value. In the seconddetection step, the detector may compute a difference between anelectro-physical quantity measured at a certain measurement time pointand an electro-physical quantity measured at another measurement timepoint directly before said certain measurement time point and determinethat liquid conduction is established between the second detectionelement and the third detection element when the difference is greaterthan a predetermined threshold value.

[0027] For example, the computation unit may compute the concentrationof the particular component based on a difference between anelectro-physical quantity measured after a predetermined time haselapsed since liquid conduction between the second detection element andthe third detection element was detected by the detector and anotherelectro-physical quantity measured when liquid conduction between thesecond detection element and the third detection element is detected bythe detector.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a view for describing a first embodiment of the presentinvention and schematically illustrates a concentration measuringapparatus to which a biosensor is attached.

[0029]FIG. 2 is a perspective view of the biosensor shown in FIG. 1.

[0030]FIG. 3 is an exploded perspective view of the biosensor shown inFIG. 2.

[0031]FIGS. 4A-4E are sectional views taken along lines IV-IV in FIG. 2for describing the movement of the blood in the capillary.

[0032]FIG. 5 is a flowchart for describing the concentration measurementoperation.

[0033]FIG. 6 is a view for describing a second embodiment of the presentinvention and schematically illustrates a concentration measuringapparatus to which a biosensor is attached.

[0034]FIG. 7 is a perspective view of the biosensor shown in FIG. 6.

[0035]FIG. 8 is an exploded perspective view of the biosensor shown inFIG. 7.

[0036]FIG. 9 is a flowchart for describing the concentration measurementoperation.

[0037]FIG. 10 is a flowchart for describing the liquid conductiondetection process in the concentration measurement operation.

[0038]FIG. 11 is an exploded perspective view illustrating an example ofprior art biosensor.

[0039]FIG. 12 is a sectional view of the biosensor shown in FIG. 11.

BEST MODE FOR CARRYING OUT THE INVENTION

[0040] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

[0041]FIGS. 1-5 illustrate a first embodiment of the present invention.

[0042] As shown in FIG. 1, a concentration measuring apparatus 1 formeasuring the concentration of a particular component in a sample liquidusing a biosensor 2 includes a controller 10, a memory 11, a switchingunit 12, a voltage application unit 13, a current measurer 14, adetector 15, a computation unit 16 and a display 17.

[0043] As shown in FIGS. 2 and 3, the biosensor 2 includes a substrate3, a first and a second spacers 40, 41, a cover 5, and a capillary 6defined by these parts.

[0044] The substrate 3 has an upper surface 30 formed with an operativeelectrode 31, a first counterpart electrode 32 and a second counterpartelectrode 33 which extend longitudinally of the substrate 3. Theelectrodes 31-33 are spaced from each other widthwise of the substrate 3and covered with an insulating film 34 except for pairs of opposite ends31 a-33 a and 31 b-33 b. The ends 31 a-33 a of the operative electrode31, first counterpart electrode 32 and second counterpart electrode 33are connected to each other via a reagent portion 35. The reagentportion 35 is in a solid state and contains oxidoreductase and anelectron carrier. The kind of oxidoreductase and electron carrier isselected depending on the kind of the component to be measured. Tomeasure e.g. the glucose level, glucose dehydrogenase or glucose oxidasemay be used as oxidoreductase, and potassium ferricyanide may be used aselectron carrier, for example.

[0045] The cover 5 is laminated on the substrate 3 via the first and thesecond spacers 40 and 41. Each of the first and the second spacers 40and 41, which are spaced from each other longitudinally of the substrate3, has a predetermined thickness and extends widthwise of the substrate3 to partially cover the substrate 3. Thus, the first and the secondspacers 40, 41 define the thickness, width, and internal configurationof the capillary 6. Specifically, the capillary 6 has an internal spaceextending widthwise of the substrate 3 and communicating with theoutside through openings 60, 61.

[0046] In the biosensor 2, when a sample liquid B is introduced throughthe opening 60, the sample liquid moves through the capillary 6 towardthe opening 61 by capillary action, as shown in FIGS. 4A-4D, andeventually fills the internal space of the capillary 6, as shown in FIG.4E. During the movement, the sample liquid B dissolves the reagentportion 35 to form a liquid phase reaction system in the capillary 6. Inthe liquid phase reaction system, oxidation-reduction reaction occurs toproduce a reaction product in accordance with the amount of thecomponent to be measured. In measuring glucose level, glucose isoxidized, while the electron carrier is reduced. When a voltage isapplied to the liquid phase reaction system by utilizing the operativeelectrode 31 and at least one of the counterpart electrodes 32 and 33,for example, the reduced electron carrier releases the electrons. Theelectrons released from the electron carrier are supplied to theoperative electrode 31.

[0047] The controller 10 shown in FIG. 1 controls the operation of eachof the units 12-17.

[0048] The memory 11 stores programs and data necessary for operatingthe units 12-17. For instance, the data stored in the memory 11 mayinclude that as to a calibration curve showing the relationship betweena response current (or the voltage converted from the current) and theglucose level, and that as to correction values used for computing theconcentration in the computation unit 16. For instance, the data as tocorrection values is stored in the form of a table or a formula asassociated with the time taken from when liquid conduction isestablished between the end 31 a of the operative electrode 31 and the32 a of the first counterpart electrode 32 till when liquid conductionis established between the end 31 a of the operative electrode 31 andthe 33 a of the second counterpart electrode 33.

[0049] The switching unit 12 includes a first switch 12 a and a secondswitch 12 b. The switches 12 a and 12 b are turned on and offindividually by the controller 10. By individually turning on or off thefirst switch 12 a and the second switch 12 b, the voltage applicationunit 13 and the current measurer 14 are electrically connected toselected one or both of the first counterpart electrode 32 and thesecond counterpart electrode 33.

[0050] The voltage application unit 13 serves to apply a voltage acrossthe operative electrode 31 and the counterpart electrodes 32, 33. Thevoltage application unit 13 includes a DC power source such as a drycell or a rechargeable battery.

[0051] The current measurer 14 measures the response current when avoltage is applied across the operative electrode 31 and at least one ofthe counterpart electrodes 32, 33.

[0052] The detector 15 detects whether or not liquid conduction isestablished between the ends 31 a of the operative electrode 31 and theend 32 a of the first counterpart electrode 32 or between the ends 31 aof the operative electrode 31 and the end 33 a of the second counterpartelectrode 33 when the sample liquid is introduced into the capillary 6.

[0053] The computation unit 16 computes the time taken from theoccurrence of liquid conduction between the end 31 a of the operativeelectrode 31 and the end 32 a of the first counterpart electrode 32 tothe occurrence of liquid conduction between the end 31 a of theoperative electrode 31 and the end 33 a of the second counterpartelectrode 33. Based on the computed time, the computation unit computesthe correction value necessary for the computation of the concentrationof the particular component in the sample liquid. The computation unitcomputes the concentration based on the correction value and the currentmeasured by the current measurer 14.

[0054] The display 17 is provided for displaying measurement results oran error message, for example. The display 17 may comprise a liquidcrystal display, for example.

[0055] Each of the controller 10, the memory 11, the detector 15 and thecomputation unit 16 may comprise one of a CPU, a ROM and a RAM or acombination of these components. Alternatively, all of the units 10, 11,15 and 16 may be provided by connecting a plurality of memories to asingle CPU.

[0056] The method for measuring the blood glucose level using theconcentration measuring apparatus 1 and biosensor 2 will be describedbelow with reference to FIGS. 1-4 and the flowchart shown in FIG. 5.Herein, it is assumed that the first and the second switches 11 a and 11b are on before the biosensor 2 is mounted to the concentrationmeasuring apparatus 1.

[0057] First, for measuring the blood glucose level, the biosensor 2 ismounted to the concentration measuring apparatus 1, and blood isintroduced into the capillary 6 of the biosensor 2 through the opening60 or the opening 61.

[0058] In the concentration measuring apparatus 1, the voltageapplication unit 13 applies a voltage across the operative electrode 31and the first counterpart electrode 32 and across the operativeelectrode 31 and the second counterpart electrode 33 of the biosensor 2(S1). The current measurer 14 measures the response current (S2).

[0059] The detector 15 checks whether or not liquid conduction isestablished between the end 31 a of the operative electrode 31 and theend 32 a of the first counterpart electrode 32 or between the end 31 aof the operative electrode 31 and the end 33 a of the second counterpartelectrode 33 (S3). Specifically, the detector 15 monitors the responsecurrent measured by the current measurer 14 and checks whether or notthe response current exceeds a predetermined threshold value. When theresponse current exceeds the threshold value, the detector 15 determinesthat the interior of the capillary is in the state as shown in FIG. 4C,for example, and that liquid conduction is established (S3: YES). Whenthe response current does not exceed the threshold value, the detector15 determines that the interior of the capillary is in the state asshown in FIG. 4A or 4B, for example, and that liquid conduction is notprovided (S3: NO).

[0060] When the detector 15 does not detect the liquid conduction (S3:NO), the current measurement in S2 and the check in S3 are repetitivelyperformed until the detector 15 detects the liquid conduction (S3: YES).In this case, the measurement of the response current in S2 is performedevery 0.05 to 0.2 seconds, for example. When the liquid conduction isnot detected even when the check is performed more than a predeterminednumber of times or even after a predetermined time has elapsed, theoperation may be treated as an error.

[0061] When the liquid conduction is detected by the detector 15 (S3:YES), It is determined that the blood has entered the capillary 6, andthe controller 10 turns off one of the first switch 12 a and the secondswitch 12 b (S4). For instance, when the liquid conduction between theend 31 a of the operative electrode 31 and the end 32 a of the firstcounterpart electrode 32 is detected, it is determined that the bloodintroduction into the capillary 6 is performed through the opening 61.In this case, the controller turns off the first switch 12 a. In thisstate, voltage application and current measurement using the operativeelectrode 31 and the second counterpart electrode 33 is possible. On theother hand, when the liquid conduction between the end 31 a of theoperative electrode 31 and the end 33 a of the second counterpartelectrode 33 is detected, it is determined that the blood introductioninto the capillary 6 is performed through the opening 60. In this case,the controller turns off the second switch 12 b. In this state, voltageapplication and current measurement using the operative electrode 31 andthe first counterpart electrode 32 is possible.

[0062] After one of the switches 12 a and 12 b is turned off, thecurrent measurer 14 measures the response current (S5), and the detector15 checks the liquid conduction again (S6). Specifically, in the casewhere the liquid conduction between the end 31 a of the operativeelectrode 31 and the end 32 a of the first counterpart electrode 32 isdetected in S3, the detector checks, in S6, whether or not liquidconduction is established between the end 31 a of the operativeelectrode 31 and the end 33 a of the second counterpart electrode 33. Onthe other hand, in the case where the liquid conduction between the end31 a of the operative electrode 31 and the end 33 a of the secondcounterpart electrode 33 is detected in S3, the detector checks, in S6,whether or not liquid conduction is established between the end 31 a ofthe operative electrode 31 and the end 32 a of the first counterpartelectrode 32. The determination of whether or not the liquid conductionis established and the process when the liquid conduction is notdetected (S6: NO) are performed similarly to S3.

[0063] When the liquid conduction is detected in S6 (S6: YES), thecomputation unit 16 computes the time taken from the detection of theliquid conduction in S3 (See FIG. 4C) to the detection of the liquidconduction in S6 (See FIG. 4D) (S7), and computes the correction valuebased on the computed time (S8). The correction value is computed basedon a lookup table stored in the memory 11 and showing the relationshipbetween the time taken and correction values. The correction value maybe one for correcting the response current (or the voltage convertedfrom the current) or one for correcting the value obtained bycomputation using a calibration curve.

[0064] In the detector 15, it is checked whether or not a predeterminedtime has elapsed since the liquid conduction was detected in S6 (S9).This check is repetitively performed until the detector 15 determinesthat the predetermined time has elapsed (S9: YES). When the detector 15determines that the predetermined time has elapsed (S9: YES), thecontroller 10 turns on the switch 12 a (or 12 b) which has turned off inS4, and the current measurer 14 measures the response current for theconcentration computation (S11). It is to be noted that the switch 12 a(or 12 b) which has turned off in S4 need not necessarily be turned onin the current measurement in S11. The measurement of response currentmay be performed at predetermined intervals after the liquid conductionis detected in S6. In this case, the response current at a certain timeafter the detection of liquid conduction in S6 may be sampled and usedas the response current for the computation. The measurement of theresponse current for the computation in S11 may be performed after apredetermined time has elapsed since the electrical conduction wasdetected in S3.

[0065] Subsequently, the computation unit 16 computes the blood glucoselevel based on the response current for the computation and thecorrection value (S12). The computation of the blood glucose level isperformed by using a calibration curve showing the relationship betweenthe response current (or the voltage converted from the current) and theblood glucose level, for example. The computation result is displayed atthe display 17 (S13).

[0066] When whole blood is used as the sample liquid, the sample liquidcontains blood cell components in addition to the component to bemeasured. The proportion of blood cell components in the blood, which isrepresented as hematocrit, influences the measurement result. As thehematocrit increases, the viscosity of the blood increases, whereby thetravel speed of the blood through the capillary 6 decreases. Therefore,when the blood glucose level is computed taking the travel speed of theblood through the capillary into consideration, a proper value whichcompensates for the influence of hematocrit can be obtained.

[0067] In this embodiment, the travel speed of the blood is found out inthe concentration measuring apparatus 1 by measuring the time taken fromthe occurrence of liquid conduction between the end 31 a of theoperative electrode 31 and the end 32 a of the first counterpartelectrode 32 to the occurrence of liquid conduction between the end 31 aof the operative electrode 31 and the end 33 a of the second counterpartelectrode 33, for example. Therefore, it is not necessary to measure thehematocrit in advance or to input the hematocrit value into theconcentration measuring apparatus 1. Therefore, it is possible to obtaina proper measurement result which compensates for the influence ofhematocrit while reducing the burden posed on the measurer or user inperforming the measurement.

[0068]FIGS. 6-10 illustrate a second embodiment of the presentinvention. In these figures, parts or elements which are identical orsimilar to those of the foregoing embodiment are designated by the samereference signs as those used for the foregoing embodiment, and detaileddescription thereof will be omitted.

[0069] As shown in FIGS. 7 and 8, the biosensor 2′ includes a substrate3′, a spacer 4′ and a cover 5′, and a capillary 6′ defined by theseparts.

[0070] The substrate 3′ has an upper surface 30′ formed with anoperative electrode 31′ and a counterpart electrode 32′. Most part ofthe operative electrode 31′ extends longitudinally of the substrate 3′,but an end 31 a′ thereof extends widthwise of the substrate 3′. Mostpart of the counterpart electrode 32′ extends longitudinally of thesubstrate 3′. The counterpart electrode 32′ has an end 32A provided witha first extension 32Aa and a second extensions 32Ab which extendwidthwise of the substrate. The second extension 32Ab is larger insurface area than the first extension 32Aa. Alternatively, the firstextension 32Aa and the second extension 32Ab may be made generally equalto each other in surface area.

[0071] The end 31 a′ of the operative electrode 31′ is located betweenthe first extension 32Aa and the second extension 32Ab. The firstextension 32Aa, the end 31 a′ and the second extension 32Ab are spacedfrom each other longitudinally of the substrate 3. A reagent portion 35is provided on the portions 31 a′, 32Aa and 32Ab to connect theseportions to each other.

[0072] The spacer 4′ serves to define the height of the capillary 6′.The spacer 4′ is formed with a slit 40′ having an open end. The slit 40′defines the width of the capillary 6′, and the open end of the slit 40′constitutes an introduction port 60′ for introducing the sample liquidinto the capillary 6′.

[0073] The cover 5′ is formed with a discharge port 50′. The dischargeport 50′ communicates with the inside of the capillary 6′ and serves todischarge air from the inside of the capillary 6′ to the outside.

[0074] Similarly to the concentration measuring apparatus 1 according tothe first embodiment shown in FIG. 1, the concentration measuringapparatus 1′ shown in FIG. 6 includes a controller 10, a memory 11, avoltage application unit 13, a current measurer 14, a detector 15, acomputation unit 16 and a display 17. However, the concentrationmeasuring apparatus 1′ shown in FIG. 6 is not provided with a switchingunit, because only the single counterpart electrode 32′ is provided inthe biosensor 2′, as shown in FIGS. 7 and 8. Part of the programs anddata stored in the memory 11 of the concentration measuring apparatus 1′differs from those of the concentration measuring apparatus 1 (See FIG.1).

[0075] The method for measuring the blood glucose level using theconcentration measuring apparatus 1′ and biosensor 2′ will be describedbelow with reference to FIGS. 6-8 and the flowcharts shown in FIGS. 9and 10.

[0076] First, for measuring the blood glucose level, the biosensor 2′ ismounted to the concentration measuring apparatus 1′, and blood isintroduced into the capillary 6′ of the biosensor 2′ through theintroduction port 60′.

[0077] In the concentration measuring apparatus 1′, the voltageapplication unit 13 applies a voltage across the operative electrode 31′and the counterpart electrode 32′ of the biosensor 2′ (S21). The currentmeasurer 14 measures a response current (S22). Based on the responsecurrent, it is determined whether or not liquid conduction isestablished between the end 31 a′ of the operative electrode 31′ and thefirst extension 32Aa of the counterpart electrode 32′ (S23).Specifically, the detector 15 monitors the response current measured bythe current measurer 12 and checks whether or not the response currentexceeds a predetermined threshold value. When the response currentexceeds the threshold value, the detector 15 determines that liquidconduction is established between the end 31 a′ of the operativeelectrode 31′ and the first extension 32Aaof the counterpart electrode32′ (S23: YES) When the response current does not exceed the thresholdvalue, the detector determines that the liquid is not provided (S23:NO).

[0078] When the detector 15 does not detect the liquid conduction (S23:NO), the current measurement in S22 and the check in S23 arerepetitively performed until the detector 15 detects the liquidconduction (S23: YES). In this case, the measurement of response currentin S22 is performed every 0.05 to 0.2 seconds, for example. When theliquid conduction is not detected even when the check is performed morethan a predetermined number of times or even after a predetermined timehas elapsed, the operation may be treated as an error.

[0079] When the liquid conduction is detected by the detector 15 (S23:YES), the detector 15 determines that the blood has entered thecapillary 6′ and checks whether or not liquid conduction is establishedbetween the end 31 a′ of the operative electrode 31′ and the secondextension 32Ab of the counterpart electrode 32′ (S24). By the processstep S24, it is determined whether or not a sufficient amount of bloodneeded for measurement is supplied to the interior of the capillary 6′.The liquid conduction detection process in S24 is performed followingthe flowchart shown in FIG. 10, for example.

[0080] Specifically, in the liquid conduction detection process, thecurrent measurer 14 measures the response current at predeterminedintervals. A response current value A is obtained in the firstmeasurement (S31), and a response current value B is obtained in thenext sampling (S32). Subsequently, the response current value A issubtracted from the response current value B to figure out the increaseα (S33). Then, a response current value C is obtained in the nextsampling (S34). The response current value B is subtracted from theresponse current value C to figure out the increase β (S35). Then,whether or not the difference between the increase β and the increase αis greater than a predetermined threshold value γ is determined (S36).When the difference between the increase β and the increase a is greaterthan the predetermined threshold value γ (S36: YES), the detector 15determines that the liquid conduction is established between the end 31a′ of the operative electrode 31′ and the second extension 32Ab of thecounterpart electrode 32′ (S37). When the difference between theincrease β and the increase a is smaller than the predeterminedthreshold value γ (S36: NO), the detector 15 determines that the liquidconduction is not provided. In this case, the process steps S31-S36 arerepeated while using the current value C (S38) as the value B, using theincrease β as the increase α (S39) and obtaining the next measurementvalue.

[0081] In the liquid phase reaction system formed in the capillary 6′,oxidation-reduction reaction proceeds. As noted above, the secondextension 32Ab of the biosensor 2′ is larger in surface area than thefirst extension 32Aa. Therefore, when the blood reaches the secondextension 32Ab, the response current value changes largely. Therefore,in the liquid conduction detection process of S24, the liquid conductionbetween the end 31 a′ of the operative electrode 31′ and the secondextension 32Ab of the counterpart electrode 32′ can be easily andreliably detected from the sharp change in the response current.

[0082] The detector 15 obtains the response current value when theliquid conduction is confirmed in S24 (S37). The response current valueis stored in the memory 11, for example. Subsequently, the detector 15checks, in Step S26, whether or not a predetermined time has elapsedsince the liquid conduction was confirmed in S24 (S37). This check isrepetitively performed until the detector 15 determines that thepredetermined time has elapsed (S26: YES). When the detector 15determines that the predetermined time has elapsed (S26: YES), thecurrent measurer 14 measures the response current for the concentrationcomputation (S27). Alternatively, the response current may be measuredat predetermined intervals after the liquid conduction is confirmed inS24 (S37). In this case, the response current at a certain time afterthe detection of liquid conduction in S24 may be sampled and used as theresponse current for computation. The obtaining of the response currentfor computation in S27 may be performed after a predetermined time haselapsed since the liquid conduction was detected in S23.

[0083] Subsequently, the computation unit 16 computes the blood glucoselevel (S28). Specifically, for example, the difference between theresponse current for computation measured in S27 and the responsecurrent measured in S25 is computed, and the blood glucose level iscomputed utilizing the difference and the calibration curve stored inthe memory 11. The computation result is displayed at the display 17(S29).

[0084] As noted above, in the prior art method, whether or not asufficient amount of blood necessary for measurement is supplied to thecapillary is determined by the comparison between a predeterminedthreshold value and a measured response current. In this embodiment, onthe other hand, the liquid conduction between the end 31 a′ of theoperative electrode 31′ and the second extension 32Ab of the counterpartelectrode 32′ is detected based on the increase of the response current(S36). Specifically, unlike the prior art method, the liquid conductionis detected based on the relative comparison between response currentvalues obtained by measurement, not based on the absolute comparisonbetween a predetermined threshold value and a response current value.Therefore, even when the response current values are influenced byhematocrit, the detection of liquid conduction can be performedaccurately without being influenced by hematocrit. Accordingly, whetheror not a sufficient amount of blood necessary for measurement issupplied to the capillary 6′ can be detected reliably.

[0085] In this embodiment, the computation of the blood glucose level inS28 is performed based on the difference between the response currentmeasured in S27 and the response current measured in S25. Since thisdifference is also a value obtained by relative comparison, thecomputation provides proper concentration value which is free from theinfluence of hematocrit.

[0086] In this embodiment, the correction similar to that of the firstembodiment may be performed. Specifically, the time taken from thedetection of liquid conduction between the end 31 a′ of the operativeelectrode 31′ and the first extension 32Aa of the counterpart electrode32′ in S23 to the confirmation of liquid conduction between the end 31a′ of the operative electrode 31′ and the second extension 32Ab of thecounterpart electrode 32′ in S24 (S37) may be computed, and correctionmay be performed based on the time taken.

[0087] The present invention is not limited to the first embodiment andthe second embodiment described above. For example, the invention isapplicable to a sample liquid other than blood, e.g. urine. Further, themethod of the present invention is applicable for measuring a componentother than glucose, e.g. cholesterol. Instead of hematocrit, the amountof chyle or the degree of hemolysis of the sample liquid may be takeninto consideration as a factor which influences the response current inthe concentration measurement of the present invention.

1. A concentration measuring method for measuring concentration of aparticular component in a sample liquid using a test tool; the test toolcomprising: a capillary for moving the sample liquid, and a firstthrough third detection elements for measuring an electro-physicalquantity, the first through the third detection elements being arrangedin the mentioned order from an upstream side toward a downstream side ina moving direction of the sample liquid; wherein the method comprises: afirst detection step for detecting whether or not liquid conduction isestablished between the first detection element and the second detectionelement; a second detection step for detecting whether or not liquidconduction is established between the second detection element and thethird detection element; a measurement step for measuring anelectro-physical quantity for computation by using at least two of thefirst through the third detection elements; and a concentrationcomputation step for computing the concentration of the particularcomponent based on the electro-physical quantity for computation.
 2. Theconcentration measuring method according to claim 1, further comprisinga time computation step for computing time taken from the detection ofliquid conduction in the first detection step to the detection of liquidconduction in the second conduction step; wherein the concentrationcomputation step comprises computing the concentration of the particularcomponent while taking the computed time into consideration.
 3. Theconcentration measuring method according to claim 2, wherein theconcentration computation step includes data processing operation forcorrecting, based on a correction value, an electro-physical quantityfor computation or a computed value obtained based on theelectro-physical quantity for computation; and wherein the correctionvalue is obtained by computation based on data showing a relationshipbetween the time taken and the correction value.
 4. The concentrationmeasuring method according to claim 1, wherein the second detection stepcomprises measuring an electro-physical quantity by using all of thefirst through the third detection elements and determining whether ornot liquid conduction is established between the second detectionelement and the third detection element based on a time history of theelectro-physical quantity.
 5. The concentration measuring methodaccording to claim 4, wherein the second detection step comprisesmeasuring an electro-physical quantity at a plurality of predeterminedmeasurement time points, computing a variation in current per unit timeat each of the measurement time points, and determining that liquidconduction is established between the second detection element and thethird detection element when the variation in current is greater than apredetermined threshold value.
 6. The concentration measuring methodaccording to claim 4, wherein the second detection step comprisescomputing a difference between an electro-physical quantity measured ata certain measurement time point and an electro-physical quantitymeasured at another measurement time point directly before said certainmeasurement time point and determining that liquid conduction isestablished between the second detection element and the third detectionelement when the difference is greater than a predetermined thresholdvalue.
 7. The concentration measuring method according to claim 4,wherein the third detection element is larger in surface area than thefirst detection element in the test tool.
 8. The concentration measuringmethod according to claim 4, wherein the concentration computation stepcomprises computing the concentration of the particular component basedon a difference between an electro-physical quantity measured after apredetermined time has elapsed since liquid conduction between thesecond detection element and the third detection element was detected inthe second detection step and another electro-physical quantity measuredwhen liquid conduction between the second detection element and thethird detection element is detected in the second step.
 9. Theconcentration measuring method according to claim 4, further comprisinga time computation step for computing time taken from the detection ofliquid conduction in the first detection step to the detection of liquidconduction in the second conduction step; wherein the concentrationcomputation step comprises computing the concentration of the particularcomponent while taking the computed time into consideration.
 10. Theconcentration measuring method according to claim 2, wherein the sampleliquid contains a coexisting component which causes an error in theconcentration measurement of the particular component; and wherein thetime taken is figured out as a reflection of influence of the coexistingcomponent.
 11. The concentration measuring method according to claim 10,wherein the sample liquid is blood containing blood cell components asthe coexisting component.
 12. The concentration measuring methodaccording to claim 11, wherein the particular component is glucose. 13.A concentration measuring apparatus for measuring concentration of aparticular component in a sample liquid using a test tool; the test toolcomprising: a capillary for moving the sample liquid, and a firstthrough a third detection elements for measuring an electro-physicalquantity, the first through the third detection elements being arrangedin the mentioned order from an upstream side toward a downstream side ina moving direction of the sample liquid; wherein the apparatuscomprises: a detector for detecting whether or not liquid conduction isestablished between the first detection element and the second detectionelement as well as between the second detection element and the thirddetection element; an electro-physical quantity measurer for measuringan electro-physical quantity for computation by using at least two ofthe first through the third detection elements; and a computation unitfor computing the concentration of the particular component based on theelectro-physical quantity for computation.
 14. The concentrationmeasuring apparatus according to claim 13, further comprising a voltageapplication unit for applying a voltage across at least two detectionelements selected from the first through the third detection elements;wherein the electro-physical quantity measurer measures a current as theelectro-physical quantity when the voltage application means applies thevoltage.
 15. The concentration measuring apparatus according to claim13, wherein the computation unit computes time taken from theestablishment of liquid conduction between the first detection elementand the second detection element to the establishment of liquidconduction between the second detection element and the third detectionelement and computes the concentration of the particular component whiletaking the computed time into consideration.
 16. The concentrationmeasuring apparatus according to claim 13, wherein the electro-physicalquantity measurer measures an electro-physical quantity at a pluralityof measurement time points with predetermined intervals, and wherein thedetector determines whether or not liquid conduction is establishedbetween the second detection element and the third detection elementbased on a time-course of the electro-physical quantity.
 17. Theconcentration measuring apparatus according to claim 16, wherein thedetector computes a variation in current per unit time at each of themeasurement time points and determines that liquid conduction isestablished between the second detection element and the third detectionelement when the variation in current is greater than a predeterminedthreshold value.
 18. The concentration measuring apparatus according toclaim 16, wherein the detector computes a difference between anelectro-physical quantity measured at a certain measurement time pointand an electro-physical quantity measured at another measurement timepoint directly before said certain measurement time point and determinesthat liquid conduction is established between the second detectionelement and the third detection element when the difference is greaterthan a predetermined threshold value.
 19. The concentration measuringapparatus according to claim 16, wherein the computation unit computesthe concentration of the particular component based on a differencebetween an electro-physical quantity measured after a predetermined timehas elapsed since liquid conduction between the second detection elementand the third detection element was detected by the detector and anotherelectro-physical quantity measured when liquid conduction between thesecond detection element and the third detection element is detected bythe detector.